1. Field of the Invention
The present invention relates to wave plate type compressor in which pistons reciprocate due to the rotation of a solid cam shaped wave plate secured to a rotary shaft.
2. Description of the Related Art
In compressors of the type that use the rotating movement of a awash plate to reciprocate pistons in their associated cylinder bores, each piston reciprocates only once for each complete revolution the swash plate makes. One way to increase the compression displacement per rotation of the swash plate, is to design larger sized compressors. Since compressors however are often mounted in vehicles, their large design is distinctly undesirable.
One proposed solution to the above shortcoming is the recently developed wave plate type compressor disclosed in Japanese Unexamined Patent Publication No. 57-110783. This compressor design uses a solid cam shaped plate, having a surface that contains wave like undulations extending in a peripheral direction. The design of this plate thus varies from that of the conventional swash plate.
The conventional wave plate type compressor will now be briefly described with reference to FIG. 15. A pair of cam surfaces 51a and 51b having predetermined widths are provided at the periphery of the front and rear surfaces of a wave plate 51. Roller 53, 54 are rotatably supported between the cam surfaces 51a, 51b and a double-headed piston 52. The contact made between rollers 53, 54 and their respective cam surfaces 51a and 51b is in a widthwise direction across the cam surfaces. When the wave plate 51 turns, therefore, the rollers 53, 54 roll on the cam surfaces 51a and 51b, so that the displacement of the cam surface 51a, caused by the rotation of the wave plate 51, is transmitted via the rollers 53, 54 to the double-headed piston 52. This in turn, causes the piston 52 to reciprocate. The cycle with which the piston 52 reciprocates can be represented according to a displacement curve of the wave plate's cam surfaces 51a and 51b. With a two cycle curve, when there are two portions on the displacement curve corresponding to top and bottom dead center positions of the piston 52, the piston 52 reciprocates twice to perform two compression cycles. During this time, the wave plate 51 makes only one complete revolution.
The above wave plate type compressor has the following disadvantages. The rollers 53, 54 are rotatably supported by the piston in such a way as to roll over the cam surfaces as the wave plate 51 turns. However, when the support portions of the piston 52 cause the rollers 53, 54 to experience a frictional resistance larger than the frictional resistance produced by the wave plate 51, the roller 53, 54 slide on the wave plate 51.
Also, the peripheral velocity, at the center of the wave plate 51 differs from that at the periphery of plate 51. The amount of the aforementioned slide tends to be more pronounced at the periphery portions of each cam surface 51a, 51b and of the wave plate 51. To promote the smooth rolling of the rollers 53, 54, a clearance is provided between the piston 52 and the rollers 53, 54. If uneven sliding occurs between the rollers 53, 54 and the associated cam surfaces, the axes of the rollers 53, 54 become inclined with respect to the wave plate 51. As a result, the rollers 53, 54 or the support portions of the pistons 52 tend to wear out quickly. This in turn contributes to the generation of compressor vibration and noise.
Furthermore, due to the limited diameters and lengths of the rollers 53, 54, the area over which the rollers 53, 54 contact the wave plate 51 is quite small. Consequently, when the piston 52 that supports the rollers 53, 54 receives a relatively large reaction force, due for example to changes in the compressor's internal gas pressure, the contact pressure of the rollers 53, 54 against the wave plate 51 is very high per unit area. This contributes to the aforementioned undesirable wearing characteristics of the rollers 53, 54 and support portions of the pistons 52.